Various applications require the formation of a seal between adjacent components such that the seal prevents the flow of fluids between the components. In some cases, the seal is disposed between first and second fluids, and the seal is configured to prevent the flow of the fluids therethrough such that the fluids do not mix. For example, FIG. 1 illustrates a conventional turbopump 10 for a rocket engine, such as the high pressure oxidizer turbopump for the space shuttle main engine, an engine built by the Rocketdyne division of The Boeing Company. The turbopump 10 includes a pump portion 12 and a turbine portion 16. A shaft 20, sometimes referred to as a “rotor,” extends between the two portions 12, 16 to mechanically couple a pump 14 in the pump portion 12 to a turbine 18 in the turbine portion 16, so that the pump 14 can be rotatably actuated by the turbine 18.
During operation, the pump 14 is used to pump cold fluids such as liquid oxygen. The turbine portion 16, however, typically operates at high temperatures, e.g., 1000° F. or greater. In some cases, additional cooling fluids are provided for cooling the turbine 18 or other components in the turbine portion 16. For example, the shaft 20 can be supported by bearings 19 positioned proximate to the turbine 18, and a coolant fluid can be provided for cooling the bearings 19. It is often desirable for the coolant fluid to be a different fluid than the fluid being pumped by the pump 14 and for the coolant fluid and the pumped fluid to remain separate in the turbopump 10. For example, if the pump 14 is used to pump liquid oxygen, and liquid hydrogen is provided to the bearings 19 as the coolant fluid, it can be necessary to prevent the mixing of the oxygen and hydrogen to prevent an undesired reaction of the two fluids. Further, although some flow of the hydrogen into the turbine 18 can be acceptable, flow of oxygen to the turbine 18 can be undesirable.
Therefore, an interpropellant seal, also referred to as an inter-fluid seal, can be provided for preventing the cryogenic oxygen from flowing from the pump portion 12 to the turbine portion 16. The interpropellant seal can include one or more labyrinth seals 22, 24, 26 disposed in a housing 28, as illustrated in FIG. 2. A gas inlet 23 can be disposed between the first and second labyrinth seals 22, 24 and configured to receive an inert gas for maintaining separation between the oxygen and hydrogen. In particular, the inert gas can flow radially inward through the inlet 23, then axially in opposite directions so that some of the gas flows toward the first labyrinth seal 22 and some flows toward the second and third seals 24, 26. The gas flowing toward the first labyrinth seal 22 mixes with the oxygen passing through the seal 22, and the oxygen and gas exit through a drain 30. Similarly, the gas flowing toward the second and third labyrinth seals 24, 26 mixes with the hydrogen passing through those seals 24, 26, and the hydrogen and/or gas exit through two drains 32, 34. Each of the drains 30, 32, 34 can include an annular space that extends circumferentially around the shaft 20, and each drain 30, 32, 34 can include a bore (not shown) that extends outward from the annular space through the housing 28 to provide a passage between the annular space and an outer surface of the housing 28.
Each labyrinth seal 22, 24, 26 typically defines a plurality of circumferentially-extending grooves that are machined into the outer surface of the shaft 20, into an outer surface of a sleeve or other component provided on the shaft 20, or into an adjacent surface on the inner diameter of the housing 28. The grooves and the clearance between the shaft 20 and housing 28 are typically designed to very specific dimensions, e.g., with tolerances of 0.001 inches or less. Variations in the dimensions of the grooves can result in an imbalance in pressure of the oxygen and hydrogen flowing through the seals 22, 24, 26 and therefore an imbalance in the flow of the inert gas. Sufficient flow of the inert gas must be maintained in both directions to prevent the oxygen and the hydrogen from flowing through the interpropellant seal. Thus, the interpropellant seal must be designed for the particular flow characteristics of the application, including the pressures and temperatures of the fluids, the dimensions of the seals 22, 24, 26, the desired flow rate of the fluids and gas, and the like. In order to achieve a desired separation of the fluids, the labyrinth seals 22, 24, 26 may be required to be long, thereby requiring space in the housing 28 along the shaft 20. Further, a significant amount of inert gas may be delivered through the interpropellant seal during operation. For a turbopump that is used on a vehicle, the added weight of the inert gas that must be carried for operation of the seal can be significant.
Thus, there exists a need for an improved sealing assembly for turbopumps and other applications requiring a fluid seal. The sealing assembly should be capable of preventing the flow of one or more fluids therethrough and for preventing the mixing of those fluids. Preferably, the seal should be relatively small and should not require an excessive amount of interpropellant gas during operation.